Gallium nitride based compound semiconductor light-emitting device having high emission efficiency and method of manufacturing the same

ABSTRACT

The present invention provides a gallium nitride based compound semiconductor light-emitting device having high light emission efficiency and a low driving voltage Vf. The gallium nitride based compound semiconductor light-emitting device includes a p-type semiconductor layer, and a transparent conductive oxide film that includes dopants and is formed on the p-type semiconductor layer. A dopant concentration at an interface between the p-type semiconductor layer and the transparent conductive oxide film is higher than the bulk dopant concentration of the transparent conductive oxide film. Therefore, the contact resistance between the p-type semiconductor layer and the transparent conductive oxide film is reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.12/097,054 which is a 371 of PCT/JP2006/324856 filed Dec. 13, 2006, andwhich claims priority from JP No. 2005-360288 and JP No. 2005-360289,both filed Dec. 14, 2005. The above-noted applications are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a gallium nitride based compoundsemiconductor light-emitting device, and more particularly, to a galliumnitride based compound semiconductor light-emitting device having a lowdriving voltage Vf and a method of manufacturing the same.

BACKGROUND ART

In recent years, gallium nitride based compound semiconductorlight-emitting devices have drawn attention as short wavelengthlight-emitting devices. The gallium nitride based compound semiconductorlight-emitting device is formed on various kinds of substrates, such asa sapphire single crystal substrate, an oxide substrate, and a III-Vgroup compound substrate, by a metal organic chemical vapor deposition(MOCVD) method or a molecular beam epitaxy (MBE) method.

The gallium nitride based compound semiconductor light-emitting deviceis characterized in that a small amount of current is diffused in thehorizontal direction. Therefore, a current is applied to only asemiconductor immediately below an electrode, and light emitted from alight-emitting layer immediately below the electrode is shielded by theelectrode, which makes it difficult to emit light from thelight-emitting device to the outside. In addition, in the light-emittingdevice, a transparent electrode is generally used as a positiveelectrode, and light is emitted to the outside through the positiveelectrode.

The positive electrode composed of the transparent electrode is formedof a known conductive material, such as Ni/Au or ITO(In₂O₃—SnO₂).Metallic materials, such as Ni/Au, have low contact resistance with ap-type semiconductor layer, but have low light transmittance. On theother hand, oxides, such as ITO, have high a light transmittance, buthave a high contact resistance.

For this reason, in the related art, the positive electrode used for thegallium nitride based compound semiconductor light-emitting device isformed by combining a contact metal layer with a metal oxide layerformed of a high conductive material, such as ITO (for example, PatentDocument 1, i.e. JP-A-9-129919).

The contact metal layer has been formed of a metallic material having alarge work function, such as Pt or Rh, in order to reduce contactresistance with the p-type semiconductor layer.

However, in the gallium nitride based compound semiconductorlight-emitting device disclosed in Patent Document 1, the contact metallayer used for the positive electrode can reduce the contact resistancewith the p-type semiconductor layer, but it is difficult to obtainsufficient light emission efficiency since the transmittance of thecontact metal layer is low, which results in low emission power.

A method of increasing the transmittance of each layer has been proposedto improve light emission efficiency and thus increase the emissionpower in the gallium nitride based compound semiconductor light-emittingdevice. In addition, another method has been proposed which improves thelight emission efficiency by forming a rough emission surface to emitlight at various angles (for example, Patent Document 2, i.e.JP-A-6-291368).

In the gallium nitride based compound semiconductor light-emittingdevice disclosed in Patent Document 2, the formation of the roughemission surface enables the light-emitting layer to have a refractiveindex of about 2.5 that is considerably higher than that of air, whichis 1, and a small threshold angle of about 25°. Therefore, it ispossible to prevent no light from being emitted to the outside due tothe repeated reflection and absorption of light in the crystal. As aresult, the light emission efficiency is improved.

However, in the gallium nitride based compound semiconductorlight-emitting device disclosed in Patent Document 2, the formation ofthe rough emission surface makes it possible to improve the lightemission efficiency, but during a process of forming the rough emissionsurface, the rough emission surface is damaged, which results in anincrease in the contact resistance with the electrode.

In order to solve the problem of the increase in the contact resistance,a light-emitting device having a low contact resistance has beenproposed in which a rough emission surface is formed on a galliumnitride based compound semiconductor light-emitting device, a metallayer including a Mg layer and a Au layer is provided in the vicinity ofthe surface of a p-type semiconductor layer, and a heat treatment isperformed to reduce the contact resistance (for example, Patent Document3, i.e. JP-A-2000-196152).

However, in the gallium nitride based compound semiconductorlight-emitting device disclosed in Patent Document 3, after the metallayer including the Mg layer and the Au layer is formed, the heattreatment needs to be performed, and the metal layer needs to beremoved. As a result, the number of processes significantly increases,and thus manufacturing costs increase. In addition, it is necessary touse a strong acid, such as aqua regia, in order to remove the Au layer.In this case, there is a fear that the surface of the gallium nitridebased compound semiconductor will be damaged.

The invention has been made in order to solve the above problems, and anobject of the invention is to provide a gallium nitride based compoundsemiconductor light-emitting device capable of obtaining high lightemission efficiency by increasing the dopant concentration of atransparent conductive oxide film, without using a contact metal layerhaving a low light transmittance for a positive electrode, and reducingcontact resistance with a p-type semiconductor layer to lower a drivingvoltage Vf, and a method of manufacturing the same.

Another object of the invention is to provide a gallium nitride basedcompound semiconductor light-emitting device capable of reducing contactresistance between a transparent conductive oxide film and a p-typesemiconductor layer having an uneven surface on at least a portionthereof to reduce a driving voltage Vf and improving light emissionefficiency, by increasing the dopant concentration of the transparentconductive oxide film, without using a contact metal layer having lowlight transmittance, and a method of manufacturing the same.

DISCLOSURE OF INVENTION

The inventors have conceived the present invention in order to solve theabove problems.

That is, the invention is as follows.

According to a first aspect of the present invention, a gallium nitridebased compound semiconductor light-emitting device includes: a galliumnitride based compound semiconductor device including a p-typesemiconductor layer; and a transparent conductive oxide film thatincludes dopants and is formed on the p-type semiconductor layer. Adopant concentration at an interface between the p-type semiconductorlayer and the transparent conductive oxide film is higher than a bulkdopant concentration of the transparent conductive oxide film.

According to a second aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according tothe first aspect, preferably, an uneven surface is formed on at least aportion of the p-type semiconductor layer.

According to a third aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according tothe first or second aspect, preferably, the dopant concentration of thetransparent conductive oxide film is the highest at the interfacebetween the transparent conductive oxide film and the p-typesemiconductor layer.

According to a fourth aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according toany one of the first to third aspects, preferably, a highly doped regionhaving a dopant concentration that is higher than that of thetransparent conductive oxide film is provided between the p-typesemiconductor layer of the gallium nitride based compound semiconductordevice and the transparent conductive oxide film.

According to a fifth aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according tothe fourth aspect, preferably, the highly doped region is formed of anyone of a dopant, a dopant oxide, and a transparent conductive materialhaving a dopant concentration that is higher than that of thetransparent conductive oxide film.

According to a sixth aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according tothe fourth or fifth aspect, preferably, the highly doped region isformed of any one of Sn, SnO₂, and ITO(In₂O₃—SnO₂) having a Snconcentration that is higher than that of the transparent conductiveoxide film.

According to a seventh aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according toany one of the first to sixth aspects, preferably, in the interfacebetween the p-type semiconductor layer of the gallium nitride basedcompound semiconductor device and the transparent conductive oxide film,a region having a dopant concentration that is higher than the bulkdopant concentration of the transparent conductive oxide film exists inthe range of 0.1 nm to 20 nm from the center of the interface.

According to an eighth aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according toany one of the first to sixth aspects, preferably, in the interfacebetween the p-type semiconductor layer of the gallium nitride basedcompound semiconductor device and the transparent conductive oxide film,a region having a dopant concentration that is higher than the bulkdopant concentration of the transparent conductive oxide film exists inthe range of 0.1 nm to 10 nm from the center of the interface.

According to a ninth aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according toany one of the first to sixth aspects, preferably, in the interfacebetween the p-type semiconductor layer of the gallium nitride basedcompound semiconductor device and the transparent conductive oxide film,a region having a dopant concentration that is higher than the bulkdopant concentration of the transparent conductive oxide film exists inthe range of 0.1 nm to 3 nm from the center of the interface.

According to a tenth aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according toany one of the first to ninth aspects, preferably, the transparentconductive oxide film is formed of at least one of ITO(In₂O₃—SnO₂),AZO(ZnO—Al₂O₃), IZO(In₂O₃—ZnO), and GZO(ZnO—GeO₂).

According to an eleventh aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according tothe tenth aspect, preferably, the transparent conductive oxide filmcontains at least ITO(In₂O₃—SnO₂).

According to a twelfth aspect of the present invention, in the galliumnitride based compound semiconductor light-emitting device according toany one of the first to eleventh aspects, preferably, the thickness ofthe transparent conductive oxide film is in the range of 35 nm to 10000nm (10 μm).

According to a thirteenth aspect of the present invention, in thegallium nitride based compound semiconductor light-emitting deviceaccording to any one of the first to eleventh aspects, preferably, thethickness of the transparent conductive oxide film is in the range of100 nm to 1000 nm (1 μm).

According to a fourteenth aspect of the present invention, there isprovided a method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device. The method includes: forming atransparent conductive oxide film including dopants on a p-typesemiconductor layer of a gallium nitride based compound semiconductordevice; and performing a thermal annealing process at a temperature inthe range of 200° C. to 900° C.

According to a fifteenth aspect of the present invention, there isprovided a method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device. The method includes: forming atransparent conductive oxide film including dopants on a p-typesemiconductor layer of a gallium nitride based compound semiconductordevice; and performing a thermal annealing process at a temperature of300° C. to 600° C.

According to a sixteenth aspect of the present invention, there isprovided a method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device. The method includes: forming atransparent conductive oxide film including dopants on a p-typesemiconductor layer of a gallium nitride based compound semiconductordevice; and performing a laser annealing process using an excimer laser.

According to a seventeenth aspect of the present invention, in themethod of manufacturing a gallium nitride based compound semiconductorlight-emitting device according to any one of the fourteenth tosixteenth aspects, preferably, before the transparent conductive oxidefilm including the dopants is formed on the p-type semiconductor layer,an uneven surface is formed on at least a portion of the p-typesemiconductor layer.

According to an eighteenth aspect of the present invention, there isprovided a method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device. The method includes: sequentiallyforming a highly doped layer and a transparent conductive oxide film ona p-type semiconductor layer of a gallium nitride based compoundsemiconductor device; and performing a thermal annealing process at atemperature in the range of 200° C. to 900° C.

According to a nineteenth aspect of the present invention, there isprovided a method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device. The method includes: sequentiallyforming a highly doped layer and a transparent conductive oxide film ona p-type semiconductor layer of a gallium nitride based compoundsemiconductor device; and performing a thermal annealing process at atemperature of 300° C. to 600° C.

According to a twentieth aspect of the present invention, in the methodof manufacturing a gallium nitride based compound semiconductorlight-emitting device according to the eighteenth or nineteenth aspect,preferably, before the highly doped layer and the transparent conductiveoxide film are sequentially formed on the p-type semiconductor layer, anuneven surface is formed on at least a portion of the p-typesemiconductor layer.

According to a twenty-first aspect of the present invention, there isprovided a method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device in which an uneven surface is formedon at least a portion of a p-type semiconductor layer of a galliumnitride based compound semiconductor device and a transparent conductiveoxide film having a high dopant concentration is formed on the p-typesemiconductor layer. The method includes: (1) a process of sequentiallyforming on a substrate an n-type semiconductor layer, a light-emittinglayer, and a p-type semiconductor layer each composed of a galliumnitride based compound semiconductor; (2) a process of forming a maskmade of metal particles on the p-type semiconductor layer; and (3) aprocess of performing dry etching on the p-type semiconductor layerusing the mask.

According to a twenty-second aspect of the present invention, in themethod of manufacturing a gallium nitride based compound semiconductorlight-emitting device according to the twenty-first aspect, preferably,the process (2) includes: forming a metal thin film on the p-typesemiconductor layer; and performing a heat treatment.

According to a twenty-third aspect of the present invention, in themethod of manufacturing a gallium nitride based compound semiconductorlight-emitting device according to the twenty-first or twenty-secondaspect, preferably, the metal particles of the mask are made of Ni, or aNi alloy.

According to a twenty-fourth aspect of the present invention, in themethod of manufacturing a gallium nitride based compound semiconductorlight-emitting device according to any one of the twenty-first totwenty-third aspects, preferably, the metal particles of the mask aremade of a metal with a low melting point or an alloy metal with a lowmelting point having a melting point in the range of 100° C. to 450° C.

According to a twenty-fifth aspect of the present invention, in themethod of manufacturing a gallium nitride based compound semiconductorlight-emitting device according to any one of the twenty-first totwenty-fourth aspects, preferably, the metal particles of the mask aremade of a metal with a low melting point selected from Ni, Au, Sn, Ge,Pb, Sb, Bi, Cd, and In, or an alloy metal with a low melting pointincluding at least one of the metallic materials.

According to a twenty-sixth aspect of the present invention, in themethod of manufacturing a gallium nitride based compound semiconductorlight-emitting device according to any one of the twenty-first totwenty-fifth aspects, preferably, the uneven surface is formed on atleast a portion of the p-type semiconductor layer by wet etching.

According to a twenty-seventh aspect of the present invention, there isprovided a lamp including the gallium nitride based compoundsemiconductor light-emitting device according to any one of the first tothirteenth aspects.

According to a twenty-eighth aspect of the present invention, there isprovided a lamp including the gallium nitride based compoundsemiconductor light-emitting device manufactured by the method accordingto any one of the fourteenth to twenty-sixth aspects.

According to the gallium nitride based compound semiconductorlight-emitting device of the above-mentioned aspects, a highly dopedregion is provided at the interface between the p-type semiconductorlayer of the gallium nitride based compound semiconductor device and thetransparent conductive oxide film. Therefore, the contact resistancebetween the p-type semiconductor layer and the transparent conductiveoxide film is reduced, and thus the driving voltage Vf is reduced. Inaddition, it is possible to obtain a gallium nitride based compoundsemiconductor light-emitting device having high light emissionefficiency.

Further, according to the gallium nitride based compound semiconductorlight-emitting device of the above-mentioned aspects, the transparentconductive oxide film is used in which a highly doped region is providedin the vicinity of only the interface between the p-type semiconductorlayer of the gallium nitride based compound semiconductor device and thetransparent conductive oxide film, and the other regions other than thehighly doped region have a dopant concentration allowing specificresistance to be the lowest. According to this structure, it is possibleto reduce the resistance of the positive electrode of the galliumnitride based compound semiconductor light-emitting device, and thusreduce the driving voltage Vf.

Furthermore, according to the gallium nitride based compoundsemiconductor light-emitting device of the above-mentioned aspects, ahigh doped region is provided at the interface between the transparentconductive oxide film and the p-type semiconductor layer having anuneven surface on at least a portion thereof. According to thisstructure, it is possible to reduce the contact resistance between thetransparent conductive oxide film and the p-type semiconductor layer,and thus reduce the driving voltage Vf. In addition, it is possible toobtain a gallium nitride based compound semiconductor light-emittingdevice having high light emission efficiency.

Moreover, according to the gallium nitride based compound semiconductorlight-emitting device of the above-mentioned aspects, the transparentconductive oxide film is used in which a highly doped region is providedin the vicinity of only the interface between the transparent conductiveoxide film and the p-type semiconductor layer having an uneven surfaceon at least a portion thereof, and the other regions other than thehighly doped region have a dopant concentration allowing specificresistance to be the lowest. According to this structure, it is possibleto reduce the resistance of the positive electrode of the galliumnitride based compound semiconductor light-emitting device, and thusreduce the driving voltage Vf. In addition, it is possible to obtain agallium nitride based compound semiconductor light-emitting devicehaving high light emission efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating thestructure of a gallium nitride based compound semiconductorlight-emitting device according to an embodiment of the presentinvention;

FIG. 2 is a plan view schematically illustrating the structure of thegallium nitride based compound semiconductor light-emitting deviceaccording to the embodiment of the present invention;

FIG. 3 is a cross-sectional view schematically illustrating a laminatedstructure of gallium nitride based compound semiconductors in thegallium nitride based compound semiconductor light-emitting deviceaccording to the embodiment of the present invention;

FIG. 4 is a graph illustrating Sn concentration values in regionsdistant from the center of the interface between a p-type GaN contactlayer and a transparent conductive oxide film layer in the galliumnitride based compound semiconductor light-emitting device according tothe embodiment of the present invention;

FIG. 5 is a diagram schematically illustrating a lamp including thegallium nitride based compound semiconductor light-emitting deviceaccording to the embodiment of the present invention;

FIG. 6 is a cross-sectional view schematically illustrating thestructure of a gallium nitride based compound semiconductorlight-emitting device according to another embodiment of the presentinvention;

FIG. 7 is a plan view schematically illustrating the structure of thegallium nitride based compound semiconductor light-emitting deviceaccording to the embodiment of the present invention;

FIG. 8 is a cross-sectional view schematically illustrating a laminatedstructure of gallium nitride based compound semiconductors in thegallium nitride based compound semiconductor light-emitting deviceaccording to the embodiment of the present invention; and

FIG. 9 is a diagram schematically illustrating a lamp including thegallium nitride based compound semiconductor light-emitting deviceaccording to the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

Hereinafter, a gallium nitride based compound semiconductorlight-emitting device according to a first embodiment of the inventionwill be described with reference to FIGS. 1 to 4.

As shown in FIG. 1, a gallium nitride based compound semiconductorlight-emitting device 101 according to this embodiment has a schematicstructure in which an n-type GaN layer 112, a light-emitting layer 113,and a p-type GaN layer (p-type semiconductor layer) 114 are laminated ona substrate 111 in this order to form a gallium nitride based compoundsemiconductor device, a positive electrode 115 composed of a transparentconductive oxide film including dopants is formed on the p-type GaNlayer 114 of the gallium nitride based compound semiconductor device,and the dopant concentration of an interface between the p-type GaNlayer 114 and the positive electrode (transparent conductive oxide film)115 is higher than the bulk dopant concentration of the transparentconductive oxide film forming the positive electrode 115.

The positive electrode composed of the transparent conductive oxide filmaccording to this embodiment of the invention can be used for a galliumnitride based compound semiconductor light-emitting device according tothe related art in which gallium nitride based compound semiconductorsare laminated on a substrate with a buffer layer interposed therebetweento form an n-type semiconductor layer, a light-emitting layer, and ap-type semiconductor layer, without any restrictions.

The substrate 111 may be formed of any known substrate materialsincluding oxide single crystals, such as sapphire single crystal (Al₂O₃;an A-plane, a C-plane, an M-plane, or an R-plane), spinel single crystal(MgAl₂O₄), ZnO single crystal, LiAlO₂ single crystal, LiGaO₂ singlecrystal, or MgO single crystal, Si single crystal, SiC single crystal,GaAs single crystal, AlN single crystal, GaN single crystal, and boridesingle crystal, such as ZrB₂. In addition, the plane direction of thesubstrate is not particularly limited. As the substrate, a justsubstrate or an off-angle substrate may be used.

The n-type GaN layer (n-type semiconductor layer) 112, thelight-emitting layer 113, and the p-type GaN layer (p-type semiconductorlayer) 114 may have various known structures. In particular, a p-typesemiconductor layer having a general carrier concentration may be used,and the transparent positive electrode 115 used in this embodiment ofthe invention may be applied to a p-type semiconductor layer having arelatively low carrier concentration of, for example, about 1×10¹⁷ cm⁻³.

As the gallium nitride based compound semiconductor, semiconductorshaving various compositions, which are represented by a general formulaAl_(x)In_(y)Ga_(1-x-y)N (0≦x<1, 0≦y<1, and 0≦x+y<1), have been known. Inthe invention, also, any of the semiconductors having variouscompositions, which are represented by the general formulaAl_(x)In_(y)Ga_(1-x-y)N (0≦x<1, 0≦y<1, and 0≦x+y<1), may be used as thegallium nitride based compound semiconductors forming the n-typesemiconductor layer, the light-emitting layer, and the p-typesemiconductor layer according to this embodiment, without anyrestrictions.

A method of growing the gallium nitride based compound semiconductor isnot particularly limited. For example, any method of growing a group-IIInitride semiconductor, such as an MOCVD (metal organic chemical vapordeposition) method, an HYPE (hydride vapor phase epitaxy) method, or anMBE (molecular beam epitaxy) method, may be used to grow the galliumnitride based compound semiconductor. The MOCVD method is preferable interms of the control of the thickness of a film and mass production. Inthe MOCVD method, hydrogen (H₂) or nitrogen (N₂) is used as a carriergas, trimethylgallium (TMG) or triethylgallium (TEG) is used as a Gasource, which is a group-III element, trimethylaluminum (TMA) ortriethyl aluminum (TEA) is used as an Al source, trimethylindium (TMI)or triethylindium (TEI) is used as an In source, and ammonium (NH₃) orhydrazine (N₂H₄) is used as a nitrogen (N) source, which is a group-Velement. In addition, for example, Si-based materials, such asmonosilane (SiH₄) and disilane (Si₂H₆), and Ge-based materials, such asgermane (GeH₄), are used as n-type dopants, and Mg-based materials, suchas bis-cyclopentadienylmagnesium (Cp₂Mg) and bisethylcyclopentadienylmagnesium ((EtCp)₂Mg), are used as p-type dopants.

As an example of the gallium nitride based compound semiconductor, agallium nitride based compound semiconductor 120 having the laminatedstructure shown in FIG. 3 may be used in which a buffer layer (notshown) made of AlN is formed on a substrate 121 made of sapphire, and aGaN underlying layer 122, an n-type GaN contact layer 123, an n-typeAlGaN clad layer 124, a light-emitting layer 125 made of InGaN, a p-typeAlGaN clad layer 126, and a p-type GaN contact layer 127 aresequentially formed on the buffer layer.

In addition, the p-type GaN contact layer 127, the p-type AlGaN cladlayer 126, the light-emitting layer 125, and the n-type AlGaN clad layer124 composed of the gallium nitride based compound semiconductors shownin FIG. 3 are partially etched such that the n-type GaN contact layer123 is exposed. Then, a known negative electrode made of, for example,Ti/Au is provided on the n-type GaN contact layer 123, and a positiveelectrode is provided on the p-type GaN contact layer 127, therebyforming a gallium nitride based compound semiconductor light-emittingdevice.

The positive electrode 115 is composed of a transparent conductive oxidefilm layer that contacts at least the p-type semiconductor layer (p-typeGaN layer 114). A positive electrode bonding pad 116 for electricalconnection to, for example, a circuit board or a lead frame is providedon a portion of the transparent conductive oxide film layer.

The transparent conductive oxide film is formed of an oxide includingdopants. For example, the transparent conductive oxide film ispreferably formed of a material having high transmittance and lowspecific resistance, such as ITO (In₂O₃—SnO₂), AZO (ZnO—Al₂O₃), IZO(ZnO—In₂O₃), or GZO (ZnO—GeO₂). In particular, ITO capable of obtaininglow specific resistance is preferably used to reduce a driving voltageVf. When AZO or GZO is used, the specific resistance thereof is higherthan that of ITO, and thus the driving voltage Vf is higher than that ofthe ITO. However, when AZO or GZO is formed on a GaN film, thecrystallinity thereof is higher than that of ITO since ZnO contained inAZO or GZO is epitaxially grown at the grain boundaries. Therefore, theuse of AZO or GZO makes it possible to form a transparent conductiveoxide film that is less peeled off and has higher strengthcharacteristics, as compared to when ITO is used.

Preferably, the transparent conductive oxide film is formed of amaterial having a composition in the vicinity of a Sn concentration atwhich the lowest specific resistance is obtained. For example, if thetransparent conductive oxide film is formed of ITO, it is preferablethat the Sn concentration of ITO be in the range of 5 to 20% by mass. Itis preferable to use ITO having a Sn concentration within the range of7.5 to 12.5% by mass in order to further reduce the specific resistance.

Further, it is preferable that the thickness of the transparentconductive oxide film be in the range of 35 nm to 10000 nm (10 μm) inorder to obtain low specific resistance and high transmittance. Inaddition, it is preferable that the thickness of the transparentconductive oxide film be less than or equal to 1000 nm (1 μm) in orderto reduce manufacturing costs.

After the transparent conductive oxide film layer is formed, a thermalannealing process is performed at a temperature in the range of 200° C.to 900° C. to diffuse the dopants uniformly contained in the transparentconductive oxide film, thereby forming a highly doped region in thevicinity of the interface between the transparent conductive oxide filmlayer and the p-type semiconductor layer. In addition, the thermalannealing process can also improve the transmittance of the transparentconductive oxide film layer.

The dopants are diffused by the thermal annealing process performed at atemperature in the range of 200° C. to 900° C. However, in order tofurther reduce contact resistance, it is preferable that the thermalannealing process be performed at a temperature in the range of 300° C.to 600° C.

The annealing process may be performed in any gas atmosphere. However,in order to improve the transmittance, it is preferable that theannealing process be performed in an atmosphere including oxygen (O₂)gas. In addition, in order to lower the specific resistance of thetransparent conductive oxide film, it is preferable that the annealingprocess be performed in an atmosphere including nitrogen (N₂) gas orhydrogen (H₂) gas.

Furthermore, a laser annealing process using an excimer laser may beperformed to diffuse the dopants in the transparent conductive oxidefilm.

It is possible to reduce the contact resistance between the positiveelectrode 115 and the p-type GaN layer 114 by forming a highly dopedregion in the vicinity of the interface between the positive electrode115 composed of the transparent conductive oxide film layer and thep-type GaN layer (p-type semiconductor layer) 114.

In the structure that reduces the contact resistance between thetransparent. conductive oxide film layer and the p-type semiconductorlayer, it is considered that the dopant concentration at which thehighest contact resistance is obtained is about 5 to 10% by mass higherthan the dopant concentration at which the transparent conductive oxidefilm has the lowest specific resistance.

When the overall dopant concentration of the transparent conductiveoxide film is increased in order to reduce the contact resistance, thespecific resistance of the transparent conductive oxide film isincreased, which results in an increase in the driving voltage Vf.However, as in this embodiment, when the dopant concentration of thetransparent conductive oxide film is increased only in the vicinity ofthe interface, it is possible to reduce the contact resistance betweenthe transparent conductive oxide film and the p-type semiconductor layerwhile maintaining low specific resistance of the transparent conductiveoxide film.

Further, since the contact resistance between the transparent conductiveoxide film layer and the p-type semiconductor layer is reduced byforming the highly doped region, it is not necessary to form a metalcontact layer in the gallium nitride based compound semiconductorlight-emitting device unlike the related art. As a result, it ispossible to prevent a reduction in transmittance due to the metalcontact layer and thus achieve a gallium nitride based compoundsemiconductor light-emitting device having high emission power.

It is preferable that the highly doped region be provided in the rangeof 0.1 nm to 20 nm from the interface between the transparent conductiveoxide film layer and the p-type semiconductor layer. In addition, inorder to further reduce the specific resistance of the transparentconductive oxide film, the highly doped region is preferably provided inthe range of 0.1 nm to 10 nm, more preferably, in the range of 0.1 nm to3 nm from the interface.

Furthermore, it is preferable that the transparent conductive oxide filmlayer have the highest dopant concentration at the interface between thetransparent conductive oxide film layer and the p-type semiconductorlayer.

A method of diffusing the dopants in the vicinity of the interface isnot limited to the method of forming the transparent conductive oxidefilm layer, but any known method may be used to diffuse the dopants. Forexample, a sputtering method or a vapor deposition method may be used toform the transparent conductive oxide film layer.

Further, it is preferable that, before the transparent conductive oxidefilm forming the positive electrode 115 according to this embodiment isformed, a cleaning process be performed on the surface of the p-type GaNlayer 114. The cleaning process performed before the transparentconductive oxide film is formed is considered to accelerate thediffusion of the dopants in the vicinity of the interface between thetransparent conductive oxide film layer and the p-type GaN layer 114,but the mechanism thereof is not clearly defined.

For example, hydrogen fluoride (HF) or hydrochloric acid (HCl) may beused to clean the surface of the p-type GaN layer 114.

Furthermore, before the transparent conductive oxide film layer isformed, a layer having a dopant concentration that is higher than thatof the transparent conductive oxide film is formed on the p-type GaNlayer 114 as a transparent conductive oxide film contact layer (notshown). In this way, it is possible to form a highly doped region in thevicinity of the interface between the positive electrode 115(transparent conductive oxide film layer) and the p-type GaN layer 114(p-type semiconductor layer).

For example, when the transparent conductive oxide film layer is formedof ITO having 10% by mass of SnO₂, the transparent conductive oxide filmcontact layer may be formed of, for example, Sn (only the dopant), SnO₂(dopant oxide), or ITO (15 to 20% by mass of SnO₂). When the transparentconductive oxide film layer is formed of AZO, the transparent conductiveoxide film contact layer may be formed of Al, Al₂O₃, or AZO (Al-rich).When the transparent conductive oxide film layer is formed of IZO, thetransparent conductive oxide film contact layer may be formed of Zn,ZnO, or IZO (Zn-rich). When the transparent conductive oxide film layeris formed of GZO, the transparent conductive oxide film contact layermay be formed of Ge, Ge₂O₅, or GZO (Ge-rich). As such, the materialforming the transparent conductive oxide film contact layer may beappropriately selected depending on the material forming the transparentconductive oxide film layer.

In this embodiment, after the transparent conductive oxide film layer isformed, the transparent conductive oxide film contact layer is formed asan independent layer between the positive electrode 115 (transparentconductive oxide film layer) and the p-type GaN layer 114 (p-typesemiconductor layer), but the invention is not limited thereto. Forexample, many highly doped regions may be provided in the transparentconductive oxide film layer.

Furthermore, since the transparent conductive oxide film contact layeris formed of the same material as that contained in the transparentconductive oxide film, the mutual diffusion therebetween easily occurs.In this case, even when a metallic material, such as Sn, is used, it isoxidized to have transmittance, which makes it possible to prevent areduction in transmittance as in the metal contact layer.

When the transparent conductive oxide film contact layer is formed, itis possible to form the highly doped region without performing heattreatment, such as a thermal annealing process or a laser annealingprocess. However, the heat treatment, such as the thermal annealingprocess or the laser annealing process, makes it possible to form thehighly doped region closer to the interface, and improve thetransmittance of the transparent conductive oxide film. For this reason,it is preferable to perform the thermal annealing process or the laserannealing process in order to reduce the driving voltage Vf or improvethe emission power of light.

The dopant concentration at the interface between the positive electrode115 and the p-type GaN layer 114 can be measured by EDS in thecross-sectional TEM that has been well known to those skilled in theart. That is, EDS is performed at a plurality of points on thecross-sectional TEM in the vicinity of the interface between thepositive electrode 115 and the p-type GaN layer 114, and it is possibleto calculate the amount of dopant from a chart for each point. When thenumber of points is insufficient to measure the dopant concentration,the number of points may be increased.

The positive electrode bonding pad 116 is formed on the positiveelectrode 115 composed of the transparent conductive oxide film layer,and has various known structures made of, for example, Au, Al, Ni, andCu. However, the material and the structure of the positive electrodebonding pad are not limited thereto.

It is preferable that the thickness of the positive electrode bondingpad 116 be in the range of 100 to 1000 nm. The bonding pad ischaracterized in that, as the thickness of the positive electrodebonding pad increases, the bondability thereof is improved. Therefore,it is more preferable that the thickness of the positive electrodebonding pad 116 be greater than or equal to 300 nm. In addition, it ismost preferable that the thickness of the positive electrode bonding pad116 be less than or equal to 500 nm in order to reduce manufacturingcosts.

A negative electrode 17 is formed so as to come into contact with then-type GaN layer 112 of the gallium nitride based compound semiconductorincluding the n-type GaN layer 112, the light-emitting layer 113, andthe p-type GaN layer 114 sequentially formed on the substrate 111.

Therefore, when the negative electrode 117 is formed, the light-emittinglayer 113 and the p-type GaN layer 114 are partially removed to exposethe n-type GaN layer 112. Then, in this embodiment, the transparentpositive electrode 115 is formed on the remaining p-type GaN layer 114,thereby forming the negative electrode 117 on the exposed n-type GaNlayer 112.

The negative electrode 117 is formed of various materials whosecompositions and structures have been known, and the present inventioncan use any of the known negative electrodes.

A known means is used to mount a transparent cover to the galliumnitride based compound semiconductor light-emitting device according tothe above-described embodiment of the present invention, thereby forminga lamp. In addition, it is possible to form a white lamp by combiningthe gallium nitride based compound semiconductor light-emitting deviceaccording to this embodiment with a cover including a phosphor.

As shown in FIG. 5, for example, the gallium nitride based compoundsemiconductor light-emitting device according to this embodiment may beused to form an LED lamp by a known method. The gallium nitride basedcompound semiconductor light-emitting device may be used for varioustypes of lamps, such as a general-purpose bomb-shaped lamp, a side viewtype lamp for a backlight of a mobile phone, and a top view type lampused for a display device. For example, when a face-up gallium nitridebased compound semiconductor light-emitting device is mounted on thebomb-shaped lamp, as shown in FIG. 5, the gallium nitride based compoundsemiconductor light-emitting device 101 is adhered to one of two frames131 and 132 by, for example, resin, and the positive electrode bondingpad and the negative electrode bonding pad are bonded to the frames 131and 132 by wires 133 and 134 formed of, for example, gold, respectively.Then, the periphery of the device is molded by a transparent resin (seea mold 135 in FIG. 5), thereby manufacturing a bomb-shaped lamp 130.

The gallium nitride based compound semiconductor light-emitting deviceaccording to this embodiment has a low driving voltage Vf and high lightemission efficiency. Therefore, it is possible to achieve ahigh-efficiency lamp.

EXAMPLES

Next, the invention will be described in more detail with reference toExamples, but the invention is not limited thereto.

Experimental Example 1

FIG. 3 is a cross-sectional view schematically illustrating an epitaxialstructure used for the gallium nitride based compound semiconductorlight-emitting device according to Examples of the invention. FIGS. 1and 2 are respectively a cross-sectional view and a plan viewschematically illustrating the gallium nitride based compoundsemiconductor light-emitting device according to the present invention.Next, the gallium nitride based compound semiconductor light-emittingdevice will be described with reference to FIGS. 1 to 3.

(Manufacture of Gallium Nitride Based Compound SemiconductorLight-Emitting Device)

The laminated structure of the gallium nitride based compoundsemiconductor light-emitting device 120 was formed by sequentiallylaminating, on a c-plane (0001) sapphire substrate 121, an undoped GaNunderlying layer (thickness=2 μm) 122, a Si-doped n-type GaN contactlayer (thickness=2 μm, and carrier concentration=1×10¹⁹ cm⁻³) 123, aSi-doped n-type Al_(0.07)Ga_(0.93)N clad layer (thickness=12.5 nm, andcarrier concentration=1×10¹⁸ cm⁻³) 124, a light-emitting layer 125having a multiple quantum structure of 6 Si-doped GaN bather layers(thickness=14.0 nm, and carrier concentration=1×10¹⁸ cm⁻³) and 5 undopedIn_(0.20)Ga_(0.80)N well layers (thickness=2.5 nm), a Mg-doped p-typeAl_(0.07)Ga_(0.93)N clad layer (thickness=10 nm) 126, and a Mg-dopedp-type GaN contact layer (thickness=100 nm) 127, with a buffer layer(not shown) formed of AlN interposed therebetween. The layers 122 to 127of the laminated structure of the gallium nitride based compoundsemiconductor light-emitting device 120 were grown by a general lowpressure MOCVD device.

The epitaxial structure of the gallium nitride based compoundsemiconductor light-emitting device 120 was used to manufacture agallium nitride based compound semiconductor light-emitting device (seeFIG. 1). First, general dry etching was performed on a region forforming an n-type electrode to expose the surface of a Si-doped n-typeGaN contact layer in only the region.

Then, HF and HCl were used to clean the surface of the p-type GaNcontact layer 127, and a transparent conductive oxide film layer made ofITO was formed on only a region for forming a positive electrode on thep-type GaN contact layer 127 by a sputtering method. The ITO film wasformed with a thickness of about 400 nm by a DC magnetron sputter. Inthe sputter, an ITO target having 10% by mass of SnO₂ was used, and theITO film was formed at a pressure of about 0.3 Pa. After the transparentconductive oxide film made of ITO was formed, it was subjected to athermal annealing process at a temperature of 600° C. for one minute. Inthis way, the positive electrode (see reference numeral 115 in FIGS. 1and 2) according to the invention was formed on the p-type GaN contactlayer 127.

The positive electrode formed by the above-mentioned method had hightransmittance, for example, a transmittance of 90% or more in awavelength range of 460 nm. The transmittance was measured by aspectrophotometer using a sample for measuring transmittance in which atransparent conductive oxide film layer having the same thickness asdescribed above was laminated on a glass plate. In addition, thetransmittance value was calculated in consideration of a transmittancevalue measured from only the glass plate.

Next, a first layer (thickness=40 nm) made of Cr, a second layer(thickness=100 nm) made of Ti, and a third layer (thickness=400 nm) madeof Au were sequentially formed on a portion of the transparentconductive oxide film layer (positive electrode) and the Si-doped n-typeGaN contact layer 123 by a vapor deposition method, thereby forming apositive electrode bonding pad and a negative electrode.

After forming the positive electrode bonding pad and the negativeelectrode, the rear surface of the sapphire substrate 111 was polishedinto a mirror surface by polishing particles, such as diamond particles.Then, the laminated structure was cut into individual square chips eachhaving a 350 μm square, and the chip was mounted to the lead frame, andthen connected to the lead frame by a gold (Au) wire.

(Measurement of Driving Voltage Vf)

A probe contacted the chip and a current of 20 mA was applied to thechip to measure a forward voltage (driving voltage: Vf). As a result,the forward voltage was 3.3 V. In addition, the emission power Pomeasured by a general integrating sphere was 10 mW, and it was foundthat light was emitted from the entire surface of the positive electrode115.

(Calculation of Sn Concentration)

A Sn concentration was estimated by EDX analysis of the cross-sectionalTEM in a region having a width of 20 nm from the center of the interfacebetween the p-type GaN contact layer 127 and the transparent conductiveoxide film layer (positive electrode), and the result was shown in FIG.4. The Sn concentration was defined by the ratio (at %) of metal atoms(In+Sn+Ga+Al) that was considered to exist in the vicinity of theinterface. The Sn concentration of the transparent conductive oxide filmwas in the range of 5 to 10 at % in the region that is 2 nm or more awayfrom the interface, and the Sn concentration was about 15 at % in theregion that is 2 nm or less away from the interface.

Experimental Examples 2 to 5

Before a transparent conductive oxide film layer made of ITO was formed,a transparent conductive oxide film contact layer with a thickness ofabout 2 nm was formed, and a gallium nitride based compoundsemiconductor light-emitting device was manufactured, similar toExperimental example 1.

Experimental Example 6

Similar to Experimental example 1, a transparent conductive oxide filmmade of ITO was formed, and a KrF (248 nm) excimer laser was used toperform a laser annealing process on the film. The laser annealingprocess was performed under the conditions of an emission area of 3×3mm, an energy of 10 mJ, and a frequency of 200 Hz at one shot.

Experimental Example 7

A transparent conductive oxide film made of ITO was formed by a vapordeposition method, and the same gallium nitride based compoundsemiconductor light-emitting device as that in Experimental example 1was manufactured.

Experimental Example 8

A transparent conductive oxide film layer was formed of AZO having 10%by mass of Al₂O₃ by a sputtering method, and the same gallium nitridebased compound semiconductor light-emitting device as that inExperimental example 1 was manufactured.

(Evaluation of Close Adhesion)

In order to evaluate the close adhesion of ITO and AZO, an ITO film andan AZO film were formed on a sapphire substrate under the sameconditions as those in Experimental examples 1 and 8, and were subjectedto a heat treatment. Then, a peeling test was performed on the films. Asthe peeling test, an acceleration test, which is a combination of amethod (JIS H8062-1992) defined by JIS and a heat sink test, wasadopted.

First, a cutter knife was used to form linear scratches on the ITO filmand the AZO film in a lattice shape at intervals of 1 mm. The scratcheswere formed to reach the surface of the sapphire substrate. Then, thesamples were heated in an oven at a temperature of 400° C. for 30minutes, rapidly cooled down in the water at a temperature of 20° C.,and then dried. These heating and cooling processes were repeated fivetimes.

Then, an adhesive tape (manufactured by Nichiban Co., Ltd: a cellophaneadhesive tape with a width of 12 mm) was closely adhered to the surfaceof the film having the scratches formed therein, and the tape was peeledoff from the surface of the film. Then, among 1 mm by 1 mm 100 latticesdefined by the scratches formed on the surface of the film, the numberof remaining lattices that were not peed off was counted. That is, when100 lattices are not peeled off, it can be determined that no film ispeeled off.

Experimental Examples 9 and 10

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 1, except that theannealing process was performed at the temperature shown in Table 1.

Experimental examples 11 and 12

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 1, except that atransparent conductive film was formed with the thickness shown in Table1.

Experimental Example 13

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 1, except that the thermalannealing process at a temperature of 600° C. was not performed.

Experimental Example 14

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 1, except that thecleaning process was not performed before a transparent conductive oxidefilm was formed.

Experimental Example 15

A Pt target was used to form a transparent conductive oxide film contactlayer with a thickness of about 0.5 nm, and a gallium nitride basedcompound semiconductor light-emitting device was manufactured, similarto Experimental example 1.

Experimental Example 16

A gallium nitride based compound semiconductor light-emitting device wasmanufactured using an AZO transparent conductive oxide film layer,similar to Experimental example 8, except that the thermal annealingprocess at a temperature of 600° C. was not performed.

Experimental examples 17 and 18

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 1, except that theannealing process was performed at the temperature shown in Table 1.

Experimental Examples 19 and 20

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 1, except that atransparent conductive film was formed with the thickness shown in Table1.

Table 1 shows the formation conditions of the positive electrodesaccording to Experimental examples 1 to 20 and device characteristics.In addition, Table 1 shows Sn concentrations at positions that are 0, 1,2, 5, and 10 nm away from the interface between the p-type GaN contactlayer and the transparent conductive oxide film layer to the transparentconductive oxide film layer.

TABLE 1 Deposition conditions Thickness of Annealing CleaningTransparent after Dopant concentration/% before Deposition ContactThickness of Transparent conductive film deposition of Devicecharacteristics 0 nm from 1 nm from 2 nm from 3 nm from 5 nm from 10 nmfrom deposition method layer contact layer conductive film (nm)electrode Vf/V Po/mW interface interface interface interface interfaceinterface Experimental HF, HCl Sputtering ITO 400 600° C., one 3.3 10 1515 8 10 7 6 example 1 minute Experimental HF, HCl Sputtering Sn 2 nm ITO400 Nothing 3.3 10 18 17 10 9 8 8 example 2 Experimental HF, HClSputtering Sn 2 nm ITO 400 600° C., one 3.2 10 20 13 7 10 6 8 example 3minute Experimental HF, HCl Sputtering SnO₂ 2 nm ITO 400 600° C., one3.2 10 17 12 9 11 9 8 example 4 minute Experimental HF, HCl SputteringITO 2 nm ITO 400 600° C., one 3.2 10 19 12 11 12 9 10 example 5 (SnO₂:minute 20% by mass) Experimental HF, HCl Sputtering ITO 400 Laser 3.3 1019 20 13 14 12 11 example 6 annealing Experimental HF, HCl Vapor ITO 400600° C., one 3.3 10 15 17 12 11 9 7 example 7 deposition minuteExperimental HF, HCl Sputtering AZO 400 600° C., one 3.5 10 16 16 8 9 77 example 8 minute Experimental HF, HCl Sputtering ITO 400 800° C., one3.3 10 21 18 17 14 10 11 example 9 minute Experimental HF, HClSputtering ITO 400 250° C., one 3.4 10 14 13 11 10 8 7 example 10 minuteExperimental HF, HCl Sputtering ITO 900 600° C., one 3.2 9 18 14 12 9 108 example 11 minute Experimental HF, HCl Sputtering ITO 60 600° C., one3.5 10 17 14 12 10 8 7 example 12 minute Experimental HF, HCl SputteringITO 400 Nothing 3.6 10 11 8 10 9 10 9 example 13 Experimental NothingSputtering ITO 400 600° C., one 3.6 10 13 14 10 10 8 10 example 14minute Experimental HF, HCl Sputtering Pt 0.5 nm   ITO 400 600° C., one3.3 7 3 6 8 8 8 8 example 15 minute Experimental HF, HCl Sputtering AZO400 Nothing 3.7 10 11 10 8 10 10 10 example 16 Experimental HF, HClSputtering ITO 400 1000° C., one 3.6 10 18 16 14 10 9 10 example 17minute Experimental HF, HCl Sputtering ITO 400 200° C., one 3.6 10 12 1011 10 9 10 example 18 minute Experimental HF, HCl Sputtering ITO 1200600° C.. one 3.2 8 18 16 15 14 10 9 example 19 minute Experimental HF,HCl Sputtering ITO 30 600° C., one 3.7 10 16 14 16 13 10 11 example 20minute

According to the evaluation results of the device characteristics shownin Table 1, in the chips subjected to the thermal annealing process at atemperature of 600° C., the Sn concentration is high at the positionthat is 2 nm or less away from the interface between the p-type GaNlayer and the ITO layer, and the driving voltage Vf is reduced (forexample, Experimental example 1).

In addition, when the thermal annealing temperature is 800° C.(Experimental example 9) or 250° C. (Experimental example 10), the Snconcentration is high at the position that is 2 nm or less away from theinterface, and the driving voltage Vf is reduced.

Further, when the thickness of the transparent conductive oxide film is900 nm (Experimental example 11) or 60 nm (Experimental example 12), theSn concentration is high at the position that is 2 nm or less away fromthe interface, and the driving voltage Vf is reduced.

Further, in the chips not subjected to the thermal annealing process, itis possible to form a region having a high Sn concentration by forming aSn contact layer before an ITO layer is formed. Therefore, the drivingvoltage Vf is reduced (Experimental example 2).

In the chip having a Sn contact layer formed therein and subjected tothe thermal annealing process, a region having a high Sn concentrationexists at a position closer to the interface. Therefore, the drivingvoltage Vf is further reduced (Experimental examples 3 to 5).

In addition, the region having a high Sn concentration also exists inthe chip subjected to a laser annealing process instead of the thermalannealing process at a temperature of 600° C. (Experimental example 6)or the chip having an ITO film formed by a vapor deposition method(Experimental example 7).

When an AZO film is formed as the transparent conductive oxide film(Experimental example 8), the driving voltage Vf is higher than thatwhen an ITO film is formed. However, like the ITO film, a region that ishighly doped with Al is formed by the thermal annealing process at atemperature of 600° C., and the driving voltage Vf is reduced. Duringthe peeling test, when the ITO film is peeled off, about 70 latticesremain. However, when the AZO film is peeled off, 100 lattices allremain. As a result, the AZO film requires a higher driving voltage Vfthan the ITO film, but has higher adhesion than the ITO film.

In Experimental example 13 in which the thermal annealing process wasnot performed after the transparent conductive oxide film is formed, noregion having a high Sn concentration existed up to 10 nm away from theinterface between the p-type GaN layer and the ITO layer. InExperimental example 13, the driving voltage Vf of the light-emittingdevice was 3.6 V.

In Experimental example 14 in which the p-type GaN layer was not cleanedbefore the transparent conductive oxide film was formed, a region havinga high Sn concentration existed up to 1 nm away from the interfacebetween the p-type GaN layer and the ITO layer. In Experimental example14, the driving voltage Vf of the light-emitting device was 3.6 V.

In Experimental example 15 in which a Pt target was used to form thetransparent conductive oxide film contact layer with a thickness ofabout 0.5 nm, the dopant concentration was 3% at the interface. InExperimental example 15, the emission power Po of the light-emittingdevice was 7 mW.

In Experimental example 16 in which the transparent conductive oxidefilm was formed of AZO and the thermal annealing process at atemperature of 600° C. was not performed, no region having a high Snconcentration existed up to 10 nm away from the interface between thep-type GaN layer and the ITO layer. In Experimental example 16, thedriving voltage Vf of the light-emitting device was 3.7 V.

In Experimental example 17 in which, after the transparent conductiveoxide film was formed, the thermal annealing temperature process wasperformed at a temperature of 1000° C., the segregation of the Snconcentration was accelerated up to 2 nm away from the interface. InExperimental example 17, the driving voltage Vf of the light-emittingdevice was 3.6 V.

In Experimental example 18 in which, after the transparent conductiveoxide film was formed, the thermal annealing process was performed at atemperature of 200° C., no region having a high Sn concentration existedis up to 10 nm away from the interface between the p-type GaN layer andthe ITO layer. In Experimental example 18, the driving voltage Vf of thelight-emitting device was 3.6 V.

In Experimental example 19 in which the transparent conductive oxidefilm was formed with a large thickness of 1200 nm, the segregation ofthe Sn concentration was accelerated up to 2 nm away from the interface.In Experimental example 19, the emission power Po of the light-emittingdevice was 8 mW.

In Experimental example 20 in which the transparent conductive oxidefilm was formed with a small thickness of 30 nm, the segregation of theSn concentration was accelerated up to 2 nm away from the interface. InExperimental example 20, the driving voltage Vf of the light-emittingdevice was 3.7 V.

The above-mentioned results proved that the gallium nitride basedcompound semiconductor light-emitting device according to the inventionhad high light emission efficiency, a low driving voltage Vf, and highdevice characteristics.

Second Embodiment

Next, a gallium nitride based compound semiconductor light-emittingdevice according to a second embodiment of the invention will bedescribed with reference to FIGS. 6 to 9. The second embodiment differsfrom the first embodiment in that convex and concave portions areprovided, but the other components are the same as those in the firstembodiment. The convex and concave portions will be mainly described inthis embodiment.

[Overall Structure of Gallium Nitride Based Compound SemiconductorLight-Emitting Device]

As shown in FIG. 6, a gallium nitride based compound semiconductorlight-emitting device 201 according to this embodiment has a schematicstructure in which an n-type GaN layer 212, a light-emitting layer 213,and a p-type GaN layer (p-type semiconductor layer) 214 are laminated ona substrate 211 in this order to form a gallium nitride based compoundsemiconductor device, an uneven surface is formed on at least a portionof the p-type GaN layer 214 of the gallium nitride based compoundsemiconductor device, a positive electrode 215 composed of a transparentconductive oxide film including dopants is formed on the p-type GaNlayer 214, and the dopant concentration of an interface between thep-type GaN layer 214 and the positive electrode (transparent conductiveoxide film) 215 is higher than the bulk dopant concentration of thetransparent conductive oxide film forming the positive electrode 215.

In addition, in the example shown in FIG. 6, a random pattern of convexportions 214 b forming the uneven surface is formed on a surface 214 aof the p-type GaN layer 214, and a surface 215 a of the positiveelectrode 215 formed on the p-type GaN layer 214 has an uneven surfaceincluding convex portions 215 b corresponding to the convex portions 214b of the p-type GaN layer 214.

As shown in FIG. 6, an uneven pattern, that is, an uneven surface isformed on at least a portion of the surface 214 a of the p-type GaNlayer 214. In the example shown in FIG. 6, a convex pattern composed ofa plurality of convex portions 214 b having periodicity is formed on thesurface 214 a of the p-type GaN layer 214 substantially at the center ofthe gallium nitride based compound semiconductor light-emitting device201 in the horizontal direction.

As a method of forming the uneven pattern on the surface 214 a of thep-type GaN layer 214, a known photolithography method may be used.

The uneven pattern formed on the surface 214 a is not limited to thepattern having periodicity shown in FIG. 6. For example, a pattern inwhich the convex portions have different sizes or a pattern in which theconvex portions are arranged at irregular intervals may be used.

The shape of the convex portion 214 b is not particularly limited. Forexample, the convex portion 214 b may be formed in various shapesincluding a cylinder, a polygonal prism, such as a triangular prism or asquare pillar, a cone, or a polygonal pyramid, such as a triangularpyramid or a quadrangular pyramid. In addition, in the cross-sectionalview shown in FIG. 6, it is preferable that the dimension W (width) ofthe bottom of the convex portion 214 b be greater than or equal to thatof the top thereof. In FIG. 6, the convex portion 214 b is configured tobe tapered from the bottom to the top.

The size of the convex portion 214 b is not particularly limited. Forexample, preferably, the width W of the bottom is in the range of 0.01μm to 3 μm. This range of the width W of the bottom makes it possible toeffectively improve light emission efficiency.

A lithography technique can be used to form the convex portion 14 b suchthat the width W of the bottom of the convex portion 214 b is smallerthan 0.01 μm. However, in this case, this process costs a great deal andthe size of the convex portion is too small to obtain sufficiently highemission efficiency.

In general, the size of the gallium nitride based compound semiconductorlight-emitting device is in the range of 100 μm to 2000 μm. Therefore,when the width W of the bottom of the convex portion 214 b is largerthan 3 μm, the surface area of the convex portion 214 b in a unit areadecreases, which makes it difficult to obtain sufficiently high emissionefficiency. It is more preferable that the width W of the bottom of theconvex portion 214 b be in the range of 0.02 μm to 2 μm.

The distance between the convex portions 214 b is not particularlylimited as long as the convex portions 214 b are arranged in a periodicpattern. It is preferable that the distance between the peaks of theconvex portions be in the range of 0.01 μm to 3 μm.

A lithography technique can be used to form the convex portion 214 bsuch that the distance between the convex portions 214 b is smaller than0.01 μm. However, in this case, this process costs a great deal, and thepattern is too dense. As a result, there is a concern that lightemission efficiency will be lowered.

Further, as described above, generally, the size of the light-emittingdevice is in the range of 100 μm to 2000 μm. When the distance betweenthe convex portions 214 b is larger than 3 μm, the surface area of theconvex portion 214 b in a unit area decreases, and it is difficult toobtain sufficiently high light emission efficiency. Therefore, it ismore preferable that the distance between the concave portions be in therange of 0.02 nm to 2 nm.

The height T of the convex portion 214 b is not particularly limited,but it is preferable that the height T of the convex portion 214 b be inthe range of 0.1 μm to 2.0 μm.

When the height T of the convex portion 214 b is smaller than 0.1 μm,the height of the convex portion is too small to obtain sufficientlyhigh light emission efficiency. On the other hand, when the height ofthe convex portion 214 b is larger than 2.0 μm, the light emissionefficiency is improved, but productivity is significantly reduced, whichis not preferable.

Therefore, it is more preferable that the convex portion 214 b be formedsuch that the relationship between the width W of the bottom and theheight T satisfies W<T. When the above-mentioned relationship issatisfied, it is possible to more effectively improve the light emissionefficiency of the gallium nitride based compound semiconductorlight-emitting device.

The positive electrode 215 is composed of the transparent conductiveoxide film layer that comes into contact with at least the p-typesemiconductor layer (p-type GaN layer 214). A positive electrode bondingpad 216 for electrical connection to, for example, a circuit board or alead frame is provided on a portion of the transparent conductive oxidefilm layer.

In the example shown in FIG. 6, the surface 215 a of the positiveelectrode 215 is composed of an uneven surface having the convexportions 215 b corresponding to the convex portions 214 b formed on thesurface of the p-type GaN layer 214.

[Method of Forming Uneven Pattern in Gallium Nitride Based CompoundSemiconductor Light-Emitting Device]

In this embodiment of the invention, a region on the p-type GaN layer inwhich the uneven pattern is formed can be provided by forming a maskmade of metal particles on the surface of the p-type GaN layer includingthe region and performing dry etching on the p-type GaN layer using themask.

The uneven pattern can be formed on the surface of the p-type GaN layerby a method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device including, for example, thefollowing processes (1) to (3):

(1) a process of sequentially laminating on a substrate an n-typesemiconductor layer, a light-emitting layer, and a p-type semiconductorlayer each composed of a gallium nitride based compound semiconductor;

(2) a process of forming a mask made of metal particles on the p-typesemiconductor layer; and

(3) a process of performing dry etching on the p-type semiconductorlayer using the mask.

Next, the processes (1) to (3) will be described.

<Process (1)>

First, an n-type semiconductor layer, a light-emitting layer, and ap-type semiconductor layer, each composed of a gallium nitride basedcompound semiconductor, are laminated on a substrate in this order. Asdescribed above, any of the materials and the methods according to therelated art may be used to form the laminated structure of the galliumnitride based compound semiconductors.

<Process (2)>

Then, a metal thin film made of metal particles is formed on the p-typeGaN layer of the laminated structure of the gallium nitride basedcompound semiconductors. The metal thin film may be formed by a generalvapor deposition apparatus.

It is preferable that the thickness of the metal thin film be in therange of 50 Å to 1000 Å in consideration of the formation of a mask inthe next process.

The metal thin film may be formed by, for example, a sputteringapparatus, instead of the vapor deposition apparatus, as long as themetal thin film can be formed with a uniform thickness within theabove-mentioned range.

The metal particles used for the metal thin film (metal particle mask)may be composed of fine particles having spherical shapes and highcohesion. For example, Ni particles or Ni alloy particles may be used asthe metal particles. In addition, metal particle materials having highcohesion and capable of improving process efficiency may be a metal witha low melting pointlic materials or alloys with a low melting point thatcontain at least one of Ni, Au, Sn, Ge, Pb, Sb, Bi, Cd, and In and havea melting point in the range of 100° C. to 450° C. It is preferable touse an AuSn alloy, an AuGe alloy, an AuSnNi alloy, and an AuGeNi alloyamong these metallic materials, and it is more preferable to use theAuSn alloy.

It has been found that the AuSn alloy is eutectic at a temperature inthe range of about 190 to 420° C. when a Sn composition ratio is in therange of about 10 to 35% by mass. In addition, it has been found thatthe alloy layer is generally in a cohesive state beyond the temperaturerange.

Next, a heat treatment is performed on the metal thin film in order toobtain the metal particle mask from the metal thin film.

The heat treatment temperature of the metal thin film depends on thekind of metallic material used. It is preferable that the heat treatmentbe performed at a temperature in the range of 100 to 600° C. for oneminute. When the heat treatment is performed on the metal thin filmunder these conditions, it is possible to obtain the metal particle maskformed on the p-type GaN layer.

The shape of the metal particle mask after the heat treatment is changedby the concentration of oxygen in the heat treatment atmosphere.

Therefore, it is possible to form a metal particle mask having a shapesuitable for improving light emission efficiency by controlling theconcentration of oxygen in the heat treatment atmosphere incorrespondence with the kind of metallic material used. In addition, itis more preferable to perform the heat treatment in an atmospherecontaining no oxygen according to the kind of metallic material, inorder to form a good mask shape.

It is preferable that the density of fine particles in the metalparticle mask be in the range of 1×10⁵ particles/mm² to 1×10⁸particles/mm². This density range makes it possible to effectivelyimprove light emission efficiency. It is more preferable that thedensity be in the range of 1×10⁶ particles/mm² to 1×10⁷ particles/mm².

In this embodiment, since the shape of the uneven pattern formed on thep-type GaN layer is defined by the shape of the metal particle mask, itis possible to control the shape of the uneven pattern by controllingthe shape of the metal particle mask.

In particular, the shape of the uneven pattern on the surface of thep-type GaN layer is greatly affected by the thickness of the metalparticle mask.

It is preferable that the thickness of the metal particle mask beforethe heat treatment be in the range of 0.005 μm to 1 μm. The optimumvalue of the thickness of the metal particle mask depends on the qualityof a material forming the metal particle mask or the quality of asealing resin used when the gallium nitride based compound semiconductorlight-emitting device according to this embodiment forms a lamp.However, when the thickness of the metal particle mask is smaller than0.005 μm, the metal particle mask cannot serve as a mask, and it isdifficult to form the uneven pattern capable of effectively emittinglight on the p-type GaN layer. On the other hand, when the thickness ofthe metal particle mask is larger than 1 μm, a cohesion effect isdeteriorated, and it is difficult to form the uneven pattern capable ofeffectively emitting light on the p-type GaN layer, as described above.

<Process (3)>

Next, dry etching is performed on the p-type GaN layer using the metalparticle mask to form a specific uneven pattern on the surface of thep-type GaN layer.

As the dry etching, general reactive ion etching (RIE) may be used. Inaddition, the kind of gas used for dry etching is not particularlylimited. However, it is preferable to perform etching using gasincluding chlorine.

In order to prevent a change in metallic cohesion shape (metal particleshape), it is preferable that the temperature of the substrate bemaintained at 100° C. or less.

In this embodiment, dry etching is performed to form the uneven patternon the surface of the p-type GaN layer, but the invention is not limitedthereto. For example, wet etching may be used.

A transparent cover is provided to the gallium nitride based compoundsemiconductor light-emitting device according to this embodiment to forma lamp by, for example, a known means. In addition, it is possible toform a white lamp by combining the gallium nitride based compoundsemiconductor light-emitting device according to this embodiment with acover including a phosphor.

For example, as shown in FIG. 9, the gallium nitride based compoundsemiconductor light-emitting device according to this embodiment may beused to form an LED lamp by any known method. The gallium nitride basedcompound semiconductor light-emitting device may be used for varioustypes of lamps, such as a general-purpose bomb-shaped lamp, a side viewtype lamp for a backlight of a mobile phone, and a top view type lampused for a display device. For example, when a face-up gallium nitridebased compound semiconductor light-emitting device is mounted to thebomb-shaped lamp, as shown in FIG. 9, the gallium nitride based compoundsemiconductor light-emitting device 1 is adhered to one of two frames231 and 232 by, for example, resin, and the positive electrode bondingpad and the negative electrode bonding pad are bonded to the frames 231and 232 by wires 233 and 234 formed of, for example, gold, respectively.Then, the periphery of the device is molded by a transparent resin (seea mold 235 in FIG. 9), thereby manufacturing a bomb-shaped lamp 230.

The gallium nitride based compound semiconductor light-emitting deviceaccording to this embodiment has a low driving voltage Vf and high lightemission efficiency. Therefore, it is possible to achieve ahigh-efficiency lamp.

EXAMPLES

Next, the invention will be described in more detail with reference toExamples, but the invention is not limited thereto.

Experimental Example 21

FIG. 8 is a cross-sectional view schematically illustrating an epitaxialstructure used for the gallium nitride based compound semiconductorlight-emitting device according to Examples of the invention. FIGS. 6and 7 are a cross-sectional view and a plan view schematicallyillustrating the gallium nitride based compound semiconductorlight-emitting device according to the invention, respectively. Next,the gallium nitride based compound semiconductor light-emitting devicewill be described with reference to FIGS. 6 to 8.

(Manufacture of Gallium Nitride Based Compound SemiconductorLight-Emitting Device)

The laminated structure of the gallium nitride based compoundsemiconductor light-emitting device 220 was formed by sequentiallylaminating, on a c-plane (0001) sapphire substrate 221, an undoped GaNunderlying layer (thickness=2 μm) 222, a Si-doped n-type GaN contactlayer (thickness=2 μm, and carrier concentration=1×10¹⁹ cm⁻³) 223, aSi-doped n-type Al_(0.07)Ga_(0.93)N clad layer (thickness=12.5 nm, andcarrier concentration=1×10¹⁸ cm⁻³) 224, a light-emitting layer 225having a multiple quantum structure of 6 Si-doped GaN barrier layers(thickness=14.0 nm, and carrier concentration=1×10¹⁸ cm⁻³) and 5 undopedIn_(0.20)Ga_(0.80)N well layers (thickness=2.5 nm), a Mg-doped p-typeAl_(0.07)Ga_(0.93)N clad layer (thickness=10 nm) 226, and a Mg-dopedp-type GaN contact layer (thickness=100 nm) 227, with a buffer layer(not shown) formed of AlN interposed therebetween. The layers 222 to 227of the laminated structure of the gallium nitride based compoundsemiconductor light-emitting device 20 were grown by a general lowpressure MOCVD device.

The epitaxial structure of the gallium nitride based compoundsemiconductor 220 was used to manufacture a gallium nitride basedcompound semiconductor light-emitting device (see FIG. 6). First,general dry etching was performed on a region for forming an n-typeelectrode to expose the surface of a Si-doped n-type GaN contact layerin only the region.

(Formation of Uneven Pattern)

Next, a known photolithography technique was used to form a resist filmon portions other than the surface of the p-type GaN layer. Then, thelaminate was put into a vapor deposition apparatus and an Au/Sn (Sn: 30%by mass) film was formed with a thickness of 15 nm.

Then, a heat treatment was performed at a temperature of 250° C. in anitrogen atmosphere to aggregate particles of the Au/Sn thin film,thereby forming a mask made of metal particles. The diameter of themetal particle was in the range of 0.2 to 1.5 μm, and a metal particlelayer (mask) having a high density of 2×10⁶ particles/mm² was formed.

Then, a patterning process using the resist film was performed such thatthe surface of the p-type GaN layer was exposed, and general dry etchingwas performed thereon.

In this case, since the metal particle mask was formed in a region forthe uneven pattern, the region was selectively etched by dry etching tohave a shape corresponding to the shape of the metal particle mask, andthe surface of the p-type GaN layer was processed into the unevenpattern having a curved surface. The convex portion was formed in acircular shape in a plan view, the average of the widths of the bottomsof the convex portions was about 0.7 μm (diameter), and the average ofthe heights T of the convex portions was about 1.0 μm. In addition, theaverage of the distances between the convex portions was 0.8 μm, and thestandard deviation of the value was 50%.

Then, HF and HCl were used to clean the surface of the p-type GaNcontact layer, and a transparent conductive oxide film layer made of ITOwas formed on only a region for forming a positive electrode on thep-type GaN contact layer by a sputtering method. The ITO layer wasformed with a thickness of about 400 nm by a DC magnetron sputter. Inthe sputter, an ITO target having 10% by mass of SnO₂ was used, and theITO film was formed at a pressure of about 0.3 Pa. After the transparentconductive oxide film made of ITO was formed, it was subjected to athermal annealing process at a temperature of 600° C. for one minute. Inthis way, the positive electrode (see reference numeral 215 in FIGS. 6and 8) according to the invention was formed on the p-type GaN contactlayer 227.

The positive electrode formed by the above-mentioned method had hightransmittance, for example, a transmittance of 90% or more in awavelength range of 460 nm. The transmittance was measured by aspectrophotometer using a sample for measuring transmittance in which atransparent conductive oxide film layer having the same thickness asdescribed above was laminated on a glass plate. In addition, thetransmittance value was calculated in consideration of a transmittancevalue measured from only the glass plate.

Next, a first layer (thickness=40 nm) made of Cr, a second layer(thickness=100 nm) made of Ti, and a third layer (thickness=400 nm) madeof Au were sequentially formed on a portion of the transparentconductive oxide film layer (positive electrode) and the Si-doped n-typeGaN contact layer 223 by a vapor deposition method, thereby forming apositive electrode bonding pad and a negative electrode.

After forming the positive electrode bonding pad and the negativeelectrode, the rear surface of the substrate 211 formed of sapphire waspolished into a mirror surface by polishing particles, such as diamondparticles. Then, the laminated structure was cut into individual squarechips each having a 350 μm square, and the chip was mounted to the leadframe, and then connected to the lead frame by a gold (Au) wire.

(Measurement of Driving Voltage Vf and Emission Power Po)

A probe contacted the chip and a current of 20 mA was applied to thechip to measure a forward voltage (driving voltage: Vf). As a result,the forward voltage was 3.3 V. In addition, the emission power Pomeasured by a general integrating sphere was 12 mW, and it was foundthat light was emitted from the entire surface of the positive electrode215.

Experimental Examples 22 to 25

Before a transparent conductive oxide film layer made of ITO was formed,a transparent conductive oxide film contact layer with a thickness ofabout 2 nm was formed, and a gallium nitride based compoundsemiconductor light-emitting device was manufactured, similar toExperimental example 21.

Experimental Example 26

Similar to Experimental example 21, a transparent conductive oxide filmmade of ITO was formed, and a KrF (248 nm) excimer laser was used toperform a laser annealing process on the film. The laser annealingprocess was performed with an emission area of 3×3 mm, an energy of 10mJ, and a frequency of 200 Hz at one shot.

Experimental Example 27

A transparent conductive oxide film made of ITO was formed by a vapordeposition method, and the same gallium nitride based compoundsemiconductor light-emitting device as that in Experimental example 21was manufactured.

Experimental Example 28

A transparent conductive oxide film layer was formed of AZO having 10%by mass of Al₂O₃ by a sputtering method, and the same gallium nitridebased compound semiconductor light-emitting device as that inExperimental example 21 was manufactured.

Experimental Examples 29 and 30

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 21, except that theannealing process was performed at the temperature shown in Table 2.

Experimental Examples 31 and 32

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 21, except that atransparent conductive film was formed with the thickness shown in Table2.

Experimental Example 33

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 21, except that a processof forming concave and convex portions on the surface of the p-type GaNlayer was not performed.

Experimental Example 34

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 21, except that thethermal annealing process at a temperature of 600° C. was not performed.

Experimental Example 35

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 21, except that thecleaning process was not performed before the transparent conductiveoxide film was formed.

Experimental Example 36

A Pt target was used to form a transparent conductive oxide film contactlayer with a thickness of about 0.5 nm, and a gallium nitride basedcompound semiconductor light-emitting device was manufactured, similarto Experimental example 1.

Experimental Example 37

A gallium nitride based compound semiconductor light-emitting device wasmanufactured using an AZO transparent conductive oxide film layer,similar to Experimental example 28, except that the thermal annealingprocess at a temperature of 600° C. was not performed.

Experimental Examples 38 and 39

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 21, except that theannealing process was performed at the temperature shown in Table 2.

Experimental Examples 40 and 41

A gallium nitride based compound semiconductor light-emitting device wasmanufactured, similar to Experimental example 21, except that atransparent conductive film was formed with the thickness shown in Table2.

Table 2 shows the formation conditions of the positive electrodesaccording to Experimental examples 21 to 40 and device characteristics.In addition, Table 2 shows Sn concentrations at positions that are 0, 1,2, 5, and 10 nm away from the interface between the p-type GaN contactlayer and the transparent conductive oxide film layer to the transparentconductive oxide film layer.

TABLE 2 Deposition conditions Surface of Thickness Thickness ofAnnealing p-type Cleaning of Transparent Transparent after Dopantconcentration/% semi- before Deposition Contact contact conductiveconductive deposition Device characteristics 0 nm from 1 nm from 2 nmfrom 3 nm from 5 nm from 10 nm from conductor deposition method layerlayer film film (nm) of elctrode Vf/V Po/mW interface interfaceinterface interface interface interface Experimental Uneven HF, HClSputtering ITO 400 600° C., one 3.3 12 16 15 8 10 7 7 example 21 minuteExperimental Uneven HF, HCl Sputtering Sn 2 nm ITO 400 Nothing 3.3 12 1717 10 11 8 8 example 22 Experimental Uneven HF, HCl Sputtering Sn 2 nmITO 400 600° C., one 3.2 12 19 13 7 9 6 9 example 23 minute ExperimentalUneven HF, HCl Sputtering SnO₂ 2 nm ITO 400 600° C., one 3.2 12 18 12 910 9 8 example 24 minute Experimental Uneven HF, HCl Sputtering ITO 2 nmITO 400 600° C., one 3.2 12 20 12 11 11 9 10 example 25 (SnO₂: minute20% by mass) Experimental Uneven HF, HCl Sputtering ITO 400 Laser 3.3 1220 20 13 12 12 11 example 26 annealing Experimental Uneven HF, HCl VaporITO 400 600° C., one 3.3 12 16 16 12 13 9 8 example 27 deposition minuteExperimental Uneven HF, HCl Sputtering AZO 400 600° C., one 3.5 12 15 158 10 7 8 example28 minute Experimental Uneven HF, HCl Sputtering ITO 400800° C., one 3.3 12 22 19 18 16 10 8 example 29 minute ExperimentalUneven HF, HCl Sputtering ITO 400 250° C., one 3.4 12 14 13 12 9 8 6example 30 minute Experimental Uneven HF, HCl Sputtering ITO 900 600°C., one 3.2 11 18 16 14 11 10 9 example 31 minute Experimental UnevenHF, HCl Sputtering ITO 60 600° C., one 3.5 12 17 18 14 12 10 8 example32 minute Experimental Uneven HF, HCl Sputtering ITO 400 600° C., one3.3 10 15 14 10 11 10 9 example 33 minute Experimental Uneven HF, HClSputtering ITO 400 Nothing 3.6 12 10 11 10 9 10 10 example 34Experimental Uneven Nothing Sputtering ITO 400 600° C., one 3.6 12 12 1310 10 8 10 example 35 minute Experimental Uneven HF, HCl Sputtering Pt0.5 nm   ITO 400 600° C., one 3.3 9 4 7 8 8 7 8 example 36 minuteExperimental Uneven HF, HCl Sputtering AZO 400 Nothing 3.7 12 12 10 8 910 10 example 37 Experimental Uneven HF, HCl Sputtering ITO 400 1000°C., one 3.7 12 20 21 18 17 14 11 example 38 minute Experimental UnevenHF, HCl Sputtering ITO 400 200° C., one 3.7 12 14 12 13 10 8 8 example39 minute Experimental Uneven HF, HCl Sputtering ITO 1200 600° C., one3.2 9 18 16 13 11 10 8 example 40 minute Experimental Uneven HF, HClSputtering ITO 30 600° C., one 3.8 12 17 16 14 11 9 8 example 41 minute

According to the evaluation results of the device characteristics shownin Table 2, in the chips subjected to the thermal annealing process at atemperature of 600° C., the Sn concentration is high at the positionthat is 2 nm or less away from the interface between the p-type GaNlayer and the ITO layer, and the driving voltage Vf is reduced (forexample, Experimental example 21).

In addition, when the thermal annealing temperature is 800° C.(Experimental example 9) or 250° C. (Experimental example 10), the Snconcentration is high at the position that is 2 nm or less away from theinterface, and the driving voltage Vf is reduced.

Further, when the thickness of the transparent conductive oxide film is900 nm (Experimental example 31) or 60 nm (Experimental example 32), theSn concentration is high at the position that is 2 nm or less away fromthe interface, and the driving voltage Vf is reduced.

Further, in the chips riot subjected to the thermal annealing process,it is possible to form a region having a high Sn concentration byforming a Sn contact layer before an ITO layer is formed. Therefore, thedriving voltage Vf is reduced (Experimental example 22).

In the chip having a Sn contact layer formed therein and subjected tothe thermal annealing process, a region having a high Sn concentrationexists at a position closer to the interface. Therefore, the drivingvoltage Vf is further reduced (Experimental examples 23 to 25).

In addition, the region having a high Sn concentration also exists inthe chip subjected to a laser annealing process instead of the thermalannealing process at a temperature of 600° C. (Experimental example 26)or the chip having an ITO film formed by a vapor deposition method(Experimental example 27).

In the chips having an uneven pattern formed on the surface of thep-type GaN layer (Experimental examples 21 to 28), the emission power isabout 2 mW higher than that when no uneven pattern is formed(Experimental example 33). Further, as described above, in the chiphaving the uneven pattern formed therein (for example, Experimentalexample 21), the Sn concentration is high at the position that is 2 nmor less away from the interface between the p-type GaN layer and the ITOlayer, and the driving voltage Vf is equal to that of the chip having nouneven pattern (Experimental example 33).

When an AZO film is formed as the transparent conductive oxide film(Experimental example 28), the driving voltage Vf is higher than thatwhen an ITO film is formed. However, like the ITO film, a region that ishighly doped with Al is formed by the thermal annealing process at atemperature of 600° C., and the driving voltage Vf is reduced. During apeeling test, when the ITO film is peeled off, about 70 lattices remain.However, when the AZO film is peeled off, 100 lattices all remain. As aresult, the AZO film requires a higher driving voltage Vf than the ITOfilm, but has higher adhesion than the ITO film.

In Experimental example 33 in which no uneven pattern is formed on thesurface of the p-type GaN layer, the driving voltage Vf was 3.3 V, andthe emission power Po was 10 mW.

In Experimental example 34 in which the thermal annealing process wasnot performed after the transparent conductive oxide film is formed, noregion having a high Sn concentration existed in the range that is up to10 nm away from the interface between the p-type GaN layer and the ITOlayer. In Experimental example 34, the driving voltage Vf of thelight-emitting device was 3.6 V.

In Experimental example 35 in which the p-type GaN layer was not cleanedbefore the transparent conductive oxide film was formed, a region havinga slightly high Sn concentration existed in the range that is 1 nm awayfrom the interface between the p-type GaN layer and the ITO layer. InExperimental example 35, the driving voltage Vf of the light-emittingdevice was 3.6 V.

In Experimental example 36 in which a Pt target was used to form thetransparent conductive oxide film contact layer with a thickness ofabout 0.5 nm, the dopant concentration was 4% at the interface. InExperimental example 36, the emission power Po of the light-emittingdevice was 9 mW.

In Experimental example 37 in which the transparent conductive oxidefilm was formed of AZO and the thermal annealing process at atemperature of 600° C. was not performed, no region having a high Snconcentration existed up to 10 nm away from the interface between thep-type GaN layer and the ITO layer. In Experimental example 37, thedriving voltage. Vf of the light-emitting device was 3.7 V.

In Experimental example 38 in which, after the transparent conductiveoxide film was formed, the thermal annealing temperature process wasperformed at a temperature of 1000° C., the segregation of the Snconcentration was accelerated up to 2 nm away from the interface. InExperimental example 38, the driving voltage Vf of the light-emittingdevice was 3.7 V.

In Experimental example 39 in which, after the transparent conductiveoxide film was formed, the thermal annealing process was performed at atemperature of 200° C., the driving voltage Vf of the light-emittingdevice was 3.7 V.

In Experimental example 40 in which the transparent conductive oxidefilm was formed with a large thickness of 1200 nm, the segregation ofthe Sn concentration was accelerated up to 2 nm away from the interface.In Experimental example 40, the emission power Po of the light-emittingdevice was 9 mW.

In Experimental example 41 in which the transparent conductive oxidefilm was formed with a small thickness of 30 nm, the segregation of theSn concentration was accelerated up to 2 nm away from the interface. InExperimental example 41, the driving voltage Vf of the light-emittingdevice was 3.8 V.

The above-mentioned results prove that the gallium nitride basedcompound semiconductor light-emitting device according to the inventionhas high light emission efficiency, a low driving voltage Vf, and highdevice characteristics.

INDUSTRIAL APPLICABILITY

The invention can be applied to a gallium nitride based compoundsemiconductor light-emitting device, particularly, a gallium nitridebased compound semiconductor light-emitting device having a low drivingvoltage Vf and a method of manufacturing the same.

1. A method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device, the method comprising: forming atransparent conductive oxide film including dopants on a p-typesemiconductor layer of a gallium nitride based compound semiconductordevice; and performing a thermal annealing process at a temperaturehigher than 300° C.
 2. The method of manufacturing a gallium nitridebased compound semiconductor light-emitting device according to claim 1,wherein performing the thermal annealing process comprises: performingthe thermal annealing process at a temperature in the range of 300° C.to 900° C.
 3. A method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device, the method comprising: forming atransparent conductive oxide film including dopants on a p-typesemiconductor layer of a gallium nitride based compound semiconductordevice; and performing a laser annealing process using an excimer laser.4. The method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device according to claim 1, wherein,before the transparent conductive oxide film including the dopants isformed on the p-type semiconductor layer, an uneven surface is formed onat least a portion of the p-type semiconductor layer.
 5. A method ofmanufacturing a gallium nitride based compound semiconductorlight-emitting device, the method comprising: sequentially forming ahighly doped layer and a transparent conductive oxide film on a p-typesemiconductor layer of a gallium nitride based compound semiconductordevice; and performing a thermal annealing process at a temperaturehigher than 300° C.
 6. The method of manufacturing a gallium nitridebased compound semiconductor light-emitting device according to claim 5,wherein performing the thermal annealing process comprises: performing athermal annealing process at a temperature in the range of 300° C. to900° C.
 7. The method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device according to claim 5, wherein,before the highly doped layer and the transparent conductive oxide filmare sequentially formed on the p-type semiconductor layer, an unevensurface is formed on at least a portion of the p-type semiconductorlayer.
 8. The method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device according to claim 6, wherein,before the highly doped layer and the transparent conductive oxide filmare sequentially formed on the p-type semiconductor layer, an unevensurface is formed on at least a portion of the p-type semiconductorlayer.
 9. A method of manufacturing a gallium nitride based compoundsemiconductor light-emitting device in which an uneven surface is formedon at least a portion of a p-type semiconductor layer of a galliumnitride based compound semiconductor device and a transparent conductiveoxide film having a high dopant concentration is formed on the p-typesemiconductor layer, the method comprising: (1) a process ofsequentially forming on a substrate an n-type semiconductor layer, alight-emitting layer, and a p-type semiconductor layer, each composed ofa gallium nitride based compound semiconductor; (2) a process of forminga mask made of metal particles on the p-type semiconductor layer; and(3) a process of performing dry etching on the p-type semiconductorlayer using the mask.
 10. The method of manufacturing a gallium nitridebased compound semiconductor light-emitting device according to claim 9,wherein the process (2) includes: forming a metal thin film on thep-type semiconductor layer; and performing a heat treatment.
 11. Themethod of manufacturing a gallium nitride based compound semiconductorlight-emitting device according to claim 9, wherein the metal particlesof the mask are made of Ni, or Ni alloy.
 12. The method of manufacturinga gallium nitride based compound semiconductor light-emitting deviceaccording to claim 10, wherein the metal particles of the mask are madeof Ni, or Ni alloy.
 13. The method of manufacturing a gallium nitridebased compound semiconductor light-emitting device according to claim 9,wherein the metal particles of the mask are made of a metal with a lowmelting point or an alloy metal with a low melting point having amelting point in the range of 100° C. to 450° C.
 14. The method ofmanufacturing a gallium nitride based compound semiconductorlight-emitting device according to claim 9, wherein the metal particlesof the mask are made of a metal with a low melting point selected fromNi, Au, Sn, Ge, Pb, Sb, Bi, Cd, and In, or an alloy metal with a lowmelting point including at least one of the metallic materials.
 15. Themethod of manufacturing a gallium nitride based compound semiconductorlight-emitting device according to claim 9, wherein the uneven surfaceis formed on at least a portion of the p-type semiconductor layer by wetetching.
 16. The method of manufacturing a gallium nitride basedcompound semiconductor light-emitting device according to claim 1,wherein the thermal annealing process is performed after forming atransparent conductive oxide film.